Reserve for Losses and Loss Adjustment Expenses - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses	$ (1,715)	$ 4,748	$ 1,699	$ 9,415
Excess and Surplus Lines | Prior accident years | From the 2015 and 2014 accident years
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses	(1,400)
Excess and Surplus Lines | Prior accident years | From the 2014, 2013, and 2008 accident years
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses		3,600
Excess and Surplus Lines | Prior accident years | From the 2016-2014 accident years
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses			4,700
Excess and Surplus Lines | Prior accident years | From the 2014-2012 accident years
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses				8,000
Specialty Admitted Insurance | Prior accident years | From the 2016 accident year
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses	(949)		(907)
Specialty Admitted Insurance | Prior accident years | From the 2013, 2011, and 2010 accident years
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses		617
Specialty Admitted Insurance | Prior accident years | From the 2013, 2012, 2011, and 2010 accident years
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses				928
Casualty Reinsurance | Prior accident years
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses	$ (2,200)	$ 520	$ (2,100)	$ 483